Dental impression materials are well known in the art and have been applied for a long time. Such materials typically possess a variety of properties including a quick setting behavior, good dimensional stability and sufficient storage stability. Generally, the materials are provided in two components to be mixed prior to use and cure by a crosslinking-reaction.
One widely used class of impression materials is based on addition- or condensation crosslinking-reactions of polyorganosiloxane containing components.
Dental impression materials containing polyorganosiloxane components are typically hydrophobic in nature. In order to make these materials more hydrophilic, the incorporation of surfactants has been proposed. Measuring the contact angle of a water drop on the surface of the mixed composition is an appropriate method to find out to which extent the composition has a hydrophilic or hydrophobic behavior.
U.S. Pat. No. 5,064,891 describes an addition curable silicon composition comprising a silicone surfactant. The water contact angle measurement has been conducted on the cured material. The water contact angles measured 3 min (minutes) after the water drop has been applied on the surface of the composition was 60° and 65°, respectively.
EP 0 729 341 A1 (corresponding to U.S. Pat. No. 5,750,589) discloses the use of a polyethercarbosilane for the hydrophilization of the impression material. The water contact angle measurement has been performed 30 min after curing of the material and values of 42° have been measured.
U.S. Pat. No. 4,657,959 contains examples of compositions containing amphoteric and ionic surfactants. With regard to non-ionic fluor-containing surfactants, perfluorinated groups are attached to a polyether moiety via a polyvalent hydrocarbonyl linking group (e.g. —C2H4— or —SO2NR— group).
Addition-curing silicone impression materials formulated with a combination of a non-ionic surfactant and a methylphenylpolysiloxane are known from U.S. Pat. No. 5,907,002. The non-ionic surfactant according to this document can possess apart from a hydrophilic group a hydrophobic group which can be either an alkyl or a fluorocarbon group. Water contact angle between 28 and 60 degree have been achieved by these formulations in the cured state.
EP 1 290 998 A1 (corresponding to U.S. Pat. No. 6,861,457 B2) describes addition-cured silicone impression material compositions, which contain an organopolysiloxane with at least two aliphatic hydrocarbon chains, a polyether with a minimum of one alkyl chain, an inorganic filling material, as well as a non-ionic nonfluorinated surfactant and/or a polyether modified silicon oil. Water contact angle measurements in the cured state were in the range of 56 to 65 degree, 1 second after setting of the drop.
EP 0 613 926 A1 (corresponding to U.S. Pat. No. 5,569,691) discloses condensation-cured polyether impression materials, which contain at least one hydrophilic agent of the group of hydrophilic silicone oils, polyethylene glycol substituted fluorinated hydrocarbons, block copolymers of ethylenoxide and propylenoxide, fatty alcohol derivatives, alkylphenyl derivatives, fatty amines, amino oxide, fatty acid glycol or glycerine derivatives, fatty acids and fatty acid monoesters. The water contact angle measurement was performed 30 minutes after setting of the impression material and water contact angles in the range of 18 to 65 degree were found.
The use of mixtures of non-ionic surfactants to improve the wettability of the cured silicone impression material is described in US 2004/0236003 A1. Herein the non-ionic surfactants applied in the dental impression material are ethoxylated linear or branched hydrocarbon alcohols and/or acids.
In the above-mentioned patent documents the water contact angles have been exclusively determined on the cured rubber materials and, thus, the introduction of surfactants aimed mainly to improve the hydrophilicity of the set materials.
WO 2007/080071 A2 describes addition-cured dental impression materials based on silicones which provided hydrophilicity in the non-cured pasty state. By application of mixtures of fluorinated surfactants and silicone surfactants water contact angles of the pasty material below 10° were obtained 40 s (seconds) after mixing of the base and catalyst paste and 3 s after setting of the drop on the surface. The non-ionic fluorinated surfactants described contain at least one partly or per-fluorinated hydrocarbon rest, which is connected via an oxygen atom, an amino or a keto group, carboxylic ester group, a phosphoric acid ester and/or amide with an (poly)alkylenoxide radical, an carbohydrate radical, an aliphatic polyhydroxy radical or a nitrogen-containing heterocyclic compound or is at least a per- or partly fluorinated rest which comprise at least one amino-oxide rest.
The fluorinated surfactants taught in WO 2007/080071 however may not be very suitable for use in dental applications. Further it was found that generally the surfactants disclosed in this reference have an adverse impact on other desirable properties of the dental composition such as storage stability of the composition. Furthermore, it was found that the fluorinated surfactants of this PCT reference typically leach out of the composition both in its cured as well as uncured state, which may lead to a less than desired accuracy of the impression and to problems of reproducibility of the impression.